Red Hat Enterprise Linux 5 Administration Unleashed

396CHAPTER 19Explaining Other Common Network ServicesFIGURE 19.3Enabling NTPCheck the Enable Network Time Protocol box. A list of NTP servers accessible over theInternet is already provided as shown in the NTP Servers frame.If the client is a desktop system or another type of computer for which the time is notcrucial, the default time server will work fine. However, if the client is a server thatrequires an accurate time source, go to http://www.ntp.org/ and http://tf.nist.gov/service/time-servers.html for a list of time servers. Be sure you have permission to connectto the time server before using it, and remember that the smaller the stratum number, themore accurate the time.To add additional servers, click Add. To remove an NTP server from the list, select it fromthe list, and click Delete. Clicking OK saves and enables the changes immediately.If you prefer command-line configuration, only the ntp RPM package is needed. NTPcomes with a default configuration file. Either modify it or create your own. To configurean NTP client, the following lines must exist in /etc/ntp.conf for each NTP server:restrict mask 255.255.255.255 nomodify notrap noqueryserver Refer to the documentation in /usr/share/doc/ntp-/ for more configurationoptions in /etc/ntp.conf.Before starting the service, roughly sync the time with a server with the followingcommand:ntpd -q